Semiconductor wafer (“wafer”) fabrication often includes exposing a wafer to a plasma to allow the reactive constituents of the plasma to modify the surface of the wafer. Such plasma processing of a wafer can be performed in a plasma processing system in which a plasma is generated by transmitting radiofrequency (RF) power through a processing gas. The wafer characteristics resulting from the plasma processing operation are dependent on the process conditions, including the plasma conditions. Because the plasma conditions are closely tied to the RF power transmission through the system, it is beneficial to have an accurate knowledge of how the RF power is transmitted through the plasma processing system. Knowledge of how the RF power is transmitted through the plasma processing system is also necessary to match one plasma processing system to another, such that the plasma intensity in each plasma processing system is substantially the same for a given power input. To this end, it is necessary to have an accurate knowledge of the dielectric properties of the plasma processing system parts through which the RF power is transmitted.
Dielectric properties of interest can include the dielectric constant, and loss tangent of a particular part. One conventional technique for measuring dielectric properties of a part includes manufacturing the part with an attached sample coupon that can be removed and subjected to dielectric property measurement. In this conventional technique the sample coupon can be of a small size relative to the actual part. Because the material composition in some parts, e.g., ceramic parts, is subject to spatial variation, there is a potential that the relatively small sample coupon may not provide a true representation of the material composition of the part as a whole. In this situation, the dielectric properties measured for the sample coupon may not be accurate with regard to the actual part as a whole. Also, the dielectric properties of a sample coupon for a given part, as reported by the manufacturer of the given part, may be measured at a frequency that is different than the frequency of the RF power to which the given part will be exposed during use. Because dielectric properties are frequency dependent, the reported dielectric properties of a given part may not be applicable to the frequency of the RF power to which the given part is to be exposed, thereby requiring an extrapolation from the reported dielectric properties of the given part and an assumption of the corresponding extrapolation error.
In view of the foregoing, a solution is needed to enable measurement of the dielectric properties of actual full-sized parts to be used in plasma processing systems, and at the operating frequency of the RF power to which the parts will be exposed during plasma processing operations.